The complexity of human transcriptome is far greater than previously anticipated. Transcript diversity can be expanded through post-transcriptional RNA processing reactions as well as extensive inter-genic transcription. The genomic organization of cisacting RNA elements regulating expression of protein coding genes and non-coding inter-genic transcripts is poorly defined. This deficiency not only hampers our understanding of how the information stored within the human genome is utilized, but also weakens the connections between post-transcriptional control of gene expression and biological processes such as cell proliferation, differentiation and even human disease. The goal of this proposal is to illuminate post-transcriptional networks coordinated by RNA binding proteins. To achieve this goal we will identify cis-acting RNA elements recognized by a complete family of phylogenetically conserved, essential RNA binding proteins on a genome-wide scale. Our application focuses on the Serine and Arginine-rich family of pre-mRNA splicing factors (SR proteins). Biochemical methods will be employed to purify SR protein-RNA complexes under conditions that preserve the physiological context of RNA-protein interactions in the intact cell. Copurifying RNA molecules will be directly identified by two independent high throughput methods, pyrosequencing and hybridization to tiled genomic microarrays. Our R01 application will address the following specific aims: (1) Comprehensively identify cis-acting RNA elements recognized by the SR protein family. (2) Determine the genomic landscape of cis-acting RNA elements recognized by SR proteins. (3) Functionally validate SR protein cis-acting RNA elements.